The present invention relates to a jitter measurement device for signals reproduced from an optical disc, which measures the jitter component of the reproduced signal of optical disc by storing digital data in accordance with an indicated modulation rule; and jitter measurement method for reproduced signal of optical disc. In addition, this invention relates to a method and device for optical disc recording and/or reproducing.
The optical disc drive which reproduces the optical disc, in which the digital data is stored, detects reforming (RF) signals, and binarizes this RF signals, then generates the digital data. Specifically, the optical disc drive binarizes the RF signals, as shown in FIG. 7 (a), at the indicated slice level, and generates the digital data as shown in FIG. 7 (b).
Furthermore, the digital data which has been modulated according to the indicated modulation method, is generally recorded in the optical disc. For examples, for so-called compact disk, provided that one cycle of digital data is T, a signal to be recorded will be modulated from a signal with the cycle of 3T to that with 11T, and the waveform of each cycle will be randomly recorded. As another example, for digital video disc, provided that one cycle of digital data is T, a signal to be recorded will be modulated from a signal with the cycle of 3T to that with 14T, and the waveform of each cycle will be randomly recorded. The optical disc drive in which the digital data which has been modulated according to the indicated modulation method, is generally recorded, reproduces a signal from the optical drive; then it binarizes this signal, and generates digital data.
By the way, the digital data which has been binarized by the optical disc drive, should be generally reproduced in the way that noise riding on cyclic direction; that is, in the way that jitter component is contained. For examples, in case of picking up only the waveform with cycle of 3T, out of the RF signals reproduced from the optical disc, the cycle of the waveform if this RF signal will be 3Txc2x1"sgr"("sgr": jitter component), in which the jitter component is contained, as against the theoretical cycle 3T.
As for the reasons why such binarized digital data is reproduced containing the jitter component, for examples, we can consider the influence of noise which is included in the recording signal of the optical disc, or the influence from the characteristic of the optical pickup which detects the signals recorded in the optical disc.
Currently, a jitter measurement device which detects the jitter component of digital data reproduced from optical disc is known. The said jitter measurement device measures the jitter component of the RF signals reproduced from the optical disc. It is used for obtaining the characteristic of the optical disc or the optical pickup.
In the following sections, we will explain the first to the third jitter measurement device, which has currently been used for measuring of the jitter component of the RF signals reproduced from optical disc.
One known jitter measurement device, which has currently been used for measuring of the jitter component, computes the time breadth of digital data as voltage value, by using integration circuit, and measures the jitter component.
FIG. 8 is a waveform diagram explaining the method of operation for the first jitter measurement device on an input RF signal. First, the input RF signal is binarized by thresholding at a slice level to generate digital data. The first jitter measurement device starts an integration circuit on the leading edge of a positive transition in the digital data. The integration circuit is stopped on the trailing edge and the voltage from the integration circuit is read out. The output voltage indicates the time breadth of the digital data.
Therefore, the said first jitter measurement device can detect the jitter value which has been converted into the voltage value ("sgr"V), by comparing the said output voltage from the integration circuit with the voltage value corresponding to the integrated cycle.e
We would remind you that the said first jitter measurement device can only detect the jitter component corresponding to the waveform of cycle 1, among the waveforms of multiple cycles, which have been modulated and recorded in the optical disc, by using one(1) integration circuit; because the characteristic of the integration circuit is determined in accordance with time constant. Namely, if the optical disc to be reproduced is a compact disc, the said first jitter measurement device can only detect the jitter component of the waveform with cycle of 3T, by using one(1) integration circuit; but it cannot detect the jitter component of the waveform with the other cycles, for example, the waveform with cycle from 4T to 11T.
A second known jitter measurement device, which has currently been used for measuring of the jitter component, has adopted a device so-called xe2x80x9ctime interval analyserxe2x80x9d. It counts the time breadth of digital data by using a high-speed clock, and detects the jitter component by using the said count output. The second jitter measurement device, as shown in FIG. 9, binarizes the RF signals at the indicated slice level, and generates the digital data. Second, the said second jitter measurement device let the clock circuit operate, as well as starts counting the clock number which is the output from the said clock circuit, at the time point when the RF signal reaches to the slice level, that is, at the leading edge of the digital data. Third, the said second jitter measurement device let the clock circuit stop at the time point when the RF signal reaches to the next slice level, that is, at the trailing edge of the digital data. The count number at this point is considered to be the time breadth of digital data for the said second jitter measurement device.
Therefore, the said second jitter measurement device can detect the jitter value, by comparing the said count number of the counter with the count number at the indicated cycle.
The third known type of jitter measurement device, which has currently been used for measuring of the jitter component, has adopted the first jitter measurement device and the said second jitter measurement device.
First, the third jitter measurement device, as shown in FIG. 10, binarizes the RF signals at the indicated slice level, and generates the digital data. During this operation, in the third second jitter measurement device, the clock circuit continues generating clock at the indicated clock frequency. Second, the said third jitter measurement device lets the clock circuit operate, as well as counts the clock number which is the output from the said clock circuit, by using a counter, at the time point when the RF signal reaches to the slice level, that is, at the leading edge of the digital data. In addition, the said third jitter measurement device starts operating the integration circuit at the said leading edge of the digital data. Third, the said third jitter measurement device stop operating the integration circuit, at the timing of the clock which has been generated immediately after the leading edge of the digital data. Then, the said third jitter measurement device measures the output voltage V1 of the integration circuit, and converts the said output voltage V1 into the time breadth, which is to be the first time breadth t1 of the digital data.
The third jitter measurement device once again starts operating the integration circuit at the timing of the clock immediately before the time point when the RF signal reaches to the next slice level, that is, at the timing of the clock immediately before the trailing edge of the digital data. Then, the said third jitter measurement device stops operating the integration circuit at the time point when the RF signal reaches to the next slice level, that is, at the trailing edge of the digital data.
The third jitter measurement device detects the count number if the counter at the trailing edge of the digital data. Based on this count number and the clock frequency stated in the above, the device computes the time breadth from the timing of the clock generated immediately before the leading edge of the digital data, to the timing of the clock generated immediately after the trailing edge of the digital data. This time breadth will be called the second time breadth t2 of the digital data. Also, the said third jitter measurement device measures the output voltage V3 of the integration circuit at the above point, and converts the said output voltage V3 into the time breadth, which is to be the third time breadth t3 of the digital data.
Therefore, the said third jitter measurement device can measure the time breadth of the digital data, by adding all of the said the first time breadth t1, the second time breadth t2, and the third time breadth t3. Furthermore, the said third jitter measurement device can detect the jitter value, by comparing the time breadth of the digital data with the theoretical value.
However, the current first to third jitter measurement devices, which have been described in the previous sections, have had the following problems:
For the said first jitter measurement device, it has been likely to be affected by noise and difficult to measure the time breadth in stable condition, because it has used the integration circuit to measure the time breadth in analog. In addition, since the said first jitter measurement device cannot measure the waveform with more than one cycle by using one integration circuit, it has required the number of the integration circuits as many as the number of the waveform with cycles to be measured, if you want to measure the jitter component of the waveform with multiple cycles. Namely, for the said first jitter measurement device, for examples, you need nine(9) integration circuits with different time constants in order to detect every jitter component of the waveform with cycles from 3T to 11T, Which have been included in a compact disc. Therefore, the said first jitter measurement device has had complex hard configuration.
For the said second jitter measurement device, since it measures the time breadth by counting clock, it has not been able to measure the shorter time breadth than the said clock cycle. In addition, since the said second jitter measurement device has used the high-speed clock, its processing circuit has had to be complex. Therefore, it has been difficult to save its cost.
For the said third jitter measurement device, it has been likely to be affected by noise and difficult to measure the time breadth in stable condition, because it has used the integration circuit to measure the time breadth in analog. In addition, since the said third jitter measurement device should have a complex circuit configuration, its cost cannot be less expensive. Also, since the said third jitter measurement device has used the integration circuit, it has required the number of the integration circuits as many as the number of the waveform with cycles to be measured Therefore, the said third jitter measurement device has had to be complex in its hard configuration.
An object of the present invention is to overcome or substantially ameliorate at least some of the disadvantages of the prior art.
To attain the above-mentioned object, the invention provides a method of measuring jitter in pulse width modulated signals previously recorded on an optical disk in units of cycles and being reproduced therefrom. The method first detects a cyclic signal reproduced from the optical disk using an optical pickup. The cyclic signal is then sampled at a predetermined sampling interval so as to define sampling points, thereby producing sample data corresponding to the signal level of the cyclic signal at each of the sampling points. The method next computes a timebreadth corresponding to a time interval for which the signal level exceeds a slice level. The timebreadth is computed by first computing a first time point at which the signal level first exceeds the slice level, by interpolating between the sampling point first exceeding the slice level and the previous sampling point. Then a second time point, at which the signal level first drops below said slice level subsequent to said first time point, is computed by interpolating between the sampling point last exceeding the slice level and the next sampling point. A first time interval is then computed corresponding to the time between the first time point and the sampling point first exceeding the slice level. A second time interval is also computed corresponding to the time between the sampling point first exceeding the slice level and the sampling point last exceeding the slice level. A third time interval is computed corresponding to the time between the second time point and the sampling point last exceeding the slice level. The timebreadth is then computed by adding the first, second, and third time intervals. Finally, a jitter measurement is calculated based upon the difference between the computed timebreadth and a cyclic window corresponding to a theoretical timebreadth of the cyclic signal as recorded.
The method may further comprise detecting a peak level of the sampled cyclic signal and computing the slice level based upon the peak level. The peak level is based upon a maximum level and the absolute value of a minimum level of the sampled cyclic signal.
In a first embodiment of the invention, the peak level must exceed one fourth of the value of a theoretical signal level for the cyclic signal.
In another embodiment, the peak level must be sustained for a time interval greater than one half a minimum cyclic window corresponding to a minimum theoretical timebreadth of the cyclic signal as recorded.
The method may additionally compute an asymmetry value for the reproduced cyclic signal by detecting and comparing a peak value for each cycle of the cyclic signal.
A further aspect of the invention provides a device for measuring jitter in pulse width modulated signals previously recorded on an optical disk in units of cycles and being reproduced therefrom. The device has an optical pickup for detecting a cyclic signal reproduced from the optical disk. An analog to digital converter is provided for sampling the cyclic signal at a predetermined sampling interval so as to define sampling points, thereby producing sample data corresponding to the signal level of the cyclic signal at each of the sampling points. The device also has an operation processing means for computing a timebreadth corresponding to a time interval for which the signal level exceeds a slice level. The timebreadth is computed by first computing a first time point at which the signal level first exceeds the slice level, by interpolating between the sampling point first exceeding the slice level and the previous sampling point. Next, a second time point is computed at which the signal level first drops below the slice level subsequent to the first time point, by interpolating between the sampling point last exceeding the slice level and the next sampling point. Further, a first time interval is computed corresponding to the time between the first time point and the sampling point first exceeding the slice level. A second time interval is next computed corresponding to the time between the sampling point first exceeding the slice level and the sampling point last exceeding the slice level. A third time interval is then computed corresponding to the time between the second time point and the sampling point last exceeding the slice level. Finally, the timebreadth is computed by adding the first, second, and third time intervals. The operation processing means then calculates a jitter measurement based upon the difference between the computed timebreadth and a cyclic window corresponding to a theoretical timebreadth of the cyclic signal as recorded.
The operation processing means of the device further detects a peak level of the sampled cyclic signal and computes said slice level based upon the peak level. The peak level is based upon a maximum level and the absolute value of a minimum level of the sampled cyclic signal.
In another embodiment of the invention, the peak level must exceed one fourth of the value of a theoretical signal level for the cyclic signal.
In still another embodiment, the peak level must be sustained for a time interval greater than one half a minimum cyclic window corresponding to a minimum theoretical timebreadth of the cyclic signal as recorded.
The device may additionally compute an asymmetry value for the reproduced cyclic signal by detecting and comparing a peak value for each cycle of the cyclic signal.